Electrodeposition of indium



dummy cathodes.

Patented Oct. 22, 1946 2,409,983 ELECTRODEPOSITION or moron William M.'Martz, Indianapolis, Ind, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application June 22, 1942,

Serial No. 448,003

This invention relates to the plating of indium and has particular application to a process and electrolyte for the electrodeposition of indium.

The primary object of my invention is to provide a new and improved electrolyte and process for the electro-deposition of indium which has certain advantages over baths and processes heretofore used for this purpose.

Other objects and advantages of my invention will become more apparent from the detailed description.

The bath or electrolyte of my invention is one of good emciency, and is one that is easy to operate and control. The allowable ranges of current densities, voltages, ranges of the constituents making up the bath, etc. for good deposits are quite broad. The bath or electrolyte of the present invention is easy to make up in the first place, is one of good conductivity, and is one which deposits indium as a bright, smooth and dense deposit. The solution is readily operated at room temperature, is clear and nearly colorless, and frequent chemical analysis and replenishment are unnecessary. Soluble indium anodes preferably are used and the cathode efiiciency in such case remains more constant than in baths requiring the use of insoluble anodes.

The new and improved solutions or electrolytes in accordance with the invention are aqueous solutions containin or made up of such compounds as indium fluoborate, indium fluosilicate, and indium fluoride.

The following procedure may be followed in preparing the indium fluoborate bath or electrolyte in accordance with the invention. Fluoboric acid is readily prepared by saturating hydrofluo ric acid with boric acid. This should be prepared in a container such as one lined with hard or soft rubber since the hydrofluoric acid will readily attack glass and the heat of the reaction will melt parafiin or wax containers. The fluoboric acid is then filtered and an aqueous solution made up in the amount of 300 cc. of the acid per liter of water. The resulting mixture is then electrolyzed using pure indium anodes and In order to speed up the process the cathodes may be surrounded by a permeable animal membrane. By this device no indium is deposited on the cathodes. The cathode current density for this electrolysis is preferably maintained at about 100-150 amperes per square foot. The voltage across the electrodes should be over 1 volt and preferably over two volts. The electrolysis is allowed to continue until the desired amount of indium is present in thebath.

21 Claims. (Cl. 204-46) The indiumcontent can be determined by suitable analysis. For example, by electro-analysis or by precipitating indium as the hydroxide, In(OH-)3, igniting the indium hydroxide and weighing as indium sesquioxide (InzOs). When the desired amount of indium is present (preferably about -90 grams per liter of solution) the bath is carefully filtered and is then ready for use. A small amount of a wetting agent such as Duponal MEDRY may be added to the bath but is not necessary. Duponal ME DRY is composed of sulfates of normal primary aliphatic alcohols having from 8 to 18 carbon atoms in the molecule and particularly sodium salts thereof.

Another method which may be used to prepare the fiuoborate bath is to dissolve indium hydroxide in fluoboric acid in the desired quantity and to add water thereto to make up an aqueous solution of the required concentration. This method is at present less desirable because of the scarcity of commerical In (OH) 3.

The bath or electrolyte may be used with con- ,siderable variation in operating conditions to form bright, smooth and dense deposits of indium. The bath may be operated at a temperature of from about 50 F.-l50 F., and at current densities of from 1-300 amperes per square foot of cathode area. The pH of the solution may range from 0.0 to 2.5 or even higher. The indium content (calculated as the metal) may vary from 1 to 100 grams per liter of solution. Preferred conditions include a quantity of indium (calculated as the metal) of from 60-90 grams per liter of solution, a bath temperature of -90 F., a current density of 10-100 amperes per square foot of cathode area, a pH value of 0.1-0.4, and anodes of pure electrolytic indium. Cast indium anodes may be used but should preferably be bagged in order to prevent small particles of indium (which become detached) from producing a rough deposit. The anode cathode ratio should be at 'least 1-1 and preferably 2-1 in favor of the anode. With a high indium concentration it is preferable to operate with a current density of 50-100 amperes per square foot of cathode area. Where indium deposits of over .0005" are desired it is advantageous to use agitation. This may be accomplished in any desired manner, as by suitable movement of the cathode or electrolyte. Smooth deposits ranging from .00001 to .025" have been produced from the indium fluoborate bath. The pH of the solution tends to rise with electrolysis and this may readily be adjusted by the addition of fluoboric acid. It has also been found that when the indium content approaches the saturation point (about 100 grams of indium metal per liter of solution) a precipitate is formed. This condition should be avoided, but should it occur it may be remedied by the addition of fluoboric acid or water. The cathode elliciency is not as high as that of the anode and consequently there is a tendency for the indium to build up in the bath. This tendency may be overcome by the use of an auxiliary, insoluble carbon anode, thus reducing the effective indium anode area, or by regulating the anode current density. The carbon anode should have the same area as that of the indium. The use of this carbon anode in no way effects the cathode deposit or efiiciency.

The fluoboric bath of this invention has the ability to produce adherent deposits of indium directly on steel or ferrous metals, whereas in most indium plating baths heretofore proposed it is necessary to use a strike or flash of copper, silver, lead or tin in order to obtain indium deposits which possess good adherence.

Advantage may be taken of the characteristics of the bath where it is desired to produce platings of indium on the inner surface of a hollow cylindrical or other hollow object immersed in the electrolyte. By using an internal anode the plating is confined largely or entirely to the inner surface of the article so that it is unnecessary to mask the outer surface. Similarly by using an external anode the plating may be confined largely or entirely to the outer surface of a hollow cylindrical or other hollow article without having to mask the internal diameter or internal surface thereof.

The articles to be plated with indium should be well cleaned before plating to insure a good bond between the plating and the base metal. A recommended procedure is to degrease the parts to be plated, then electro-clean the same in an alkaline solution, then thoroughly rinse in water and thereafter electrodeposit the indium thereon. If desired, an acid dip may be given the parts after the rinse in water following the cleaning in the alkaline solution. If such acid dip is used the parts are again rinsed in water prior to plating indium thereon.

By the use or my plating solution and process indium may be electrodeposited on cathodes of various metals. The invention is particularly advantageous in plating bearings and bearing metals or alloys to render the same corrosionresistant. For example such bearing materials as lead and certain alloys of lead such as copperlead, as well as other bearing materials as cadmium and alloys thereof, may be plated with a thin coating of indium in order to protect the bearing. from corrosive products in lubricants. The indium plated bearing may be thereafter heat treated at a temperature on the order of 340 F. (or somewhat above this) in order to cause the indium to diffuse into or alloy with the base metal.

While I have described a preferred embodiment of my invention I am aware that many changes may be made and numerous details varied without departing from the principles of my invention.

I claim:

1. A process for the electrodeposition of indium which comprises passing electric current through an electrolyte composed essentially of an aqueous acid solution containing atleast one compound of the class of compounds eonsisting'of indium 4 fluoborate, indium fiuosilicate, and indium fluoride.

2. An electrolyte for the electrodeposition of indium which comprises an aqueous acid solution consisting essentially of at least one compound of the class of compounds consisting of indium fluoborate, indium fiuosilicate, and indium fluoride.

3. A process for the electrodeposition of indium which comprises passin electric current from an anode to a cathode through an electroxlyte consisting essentially of an aqueous acid solution of indium fluoborate.

4. An electrolyte for the electrodeposition of indium which consists essentially of an aqueous acid solution of indium fluoborate.

5. A process for the electrodeposition of indium which comprises passing electric current from an anode to a cathode through an electrolyte composed of an aqueous acid solution of indium fiuoborate at a temperature of about 50 F.- 150 F. and with a current density of 1-300 amperes per square foot, said solution having a. pH of 0.0-2.5 and containing 1-100 grams of indium per liter of solution. 6. A process for the electrodeposition of indium which comprises passing electric current from an anode to a cathode through an electrolyte composed of an aqueous acid solution of indium fluoborate at a temperature of about '70-90 F. and with a current density of 10-100 amperes per square foot, said solution having a pH of 0.1-0.4 and containing 69-90 grams of indium per liter of solution.

7. A process as in claim 5 in which the bath is agitated during operation.

8. A process as in claim 5 in which the anode is composed of indium.

9. A process as in claim 6 in which the bath is agitated during operation.

10. A process as in claim 3 in which the anode is composed of indium.

11. A process for electrodeposition of indium onto a portion of the surface of a cathode which comprises arranging an anode in close proximity to a surface of the cathode to be plated, and passing an electric current from the anode to the surface portion of the cathode through an electrolyte including an aqueous acid solution of indium fluoborate whereby the plating is largely or entirely concentrated on said surface without the necessity of making the remaining portions of the cathode on which no plating is desired.

12. A process as in claim 11 in which the oathode is a hollow cylinder and the anode is internally located with respect to the hollow cylinder whereby the plating is largely or entirely confined to the interior of the hollow cylinder.

13. A process as in claim 11 in which the cathode is a hollow cylinder and the anode is externally arranged with respect to the hollow cylinder whereby the plating is largely or entirely confined to the exterior surface of the hollow cy inder.

14. A process as in claim 3 in which the oathode is of steel or ferrous metal.

15. An electrolyte for electrodeposition of in- .dium which consists essentially of an aqueous acid solution of indium fluoborate, said solution containing 1-100 grams of indium per liter of solution. v

16. An electrolyte as in claim 15 in which the solution has a pH of 0.0 to about 2.5 and is maintained'at a temperature of 50150 F. during electrolysis.

17,-An electrolyte for electrodeposition of indium consisting substantially of an aqueous fluoboric acid soltuion of indium fluoborate, said solution containing 1-100 grams of indium per liter of solution.

18. A process for electrodeposition of indium which includes passing electric current from an anode to a cathode at a current density between 1 and 300 amperes per square foot of cathode area through an electrolyte consisting substantially of an aqueous fiuoboric acid solution of indium fluoborate maintained at a temperature between about 50-150 F., said electrolyte containing between 1 and 100 grams of indium per liter and having a pH between 0.0 and 2.5.

19. An electrolyte for electrodeposition of indium which includes an aqueous fiuoboric acid solution of indium fluoborate, the solution containing between 1 and 100 grams of indium per liter of solution and having a pH between 0.0 and 2.5.

20. An electrolyte for the electrodeposition of indium consisting essentially of an aqueous fluoboric acid solution of indium fluoborate, said solution containing 100 grams of indium per liter of solution.

21. An electrolyte for the electrodeposition of indium consisting essentially of an aqueous fluoboric acid solution of indium'fluoborate.

WILLIAM M. MARTZ. 

